Unidirectional antenna system



Filed June 2, 1928 F/al.

*7'0 HECK/VER ANZ Patented Jan. 12,v 1932 UNrraD STATES PATENTI GFFCE EDMOND BRUCE, RED BANK, NEW JERSEY, ASSIGNOR TO BELL TELEPHONE LABO- RATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPOETION OF NEW YORK UNIDIRECTIONAL ANTENNA SYSTEM Application filed .Tune 2, 1928. Serial No. 282,382.

This invention relates to unidirectional antenna systems, especially as adapted for transmission or reception of relatively short waves.

It has been known or some time that unilateral directivity may be achieved by a rectilinear antenna array,'comprising two or more antennae extending in a direction parallel to the direction of propagation, the ener- U gizing or receiving circuit being directly associated with one only of the antenna units of the array, the other units (there may be but one) therefore functioning as reflecting or reradiating antennae. f If the inter-antenna spacing is a quarter wave length or an odd multiplethereof, and if further the receiving or energizing circuit is connected to an end antenna unit there will be coincidence otphase at the receiver for waves propagated in one direction and opposition of phase for waves propagated in the converse direction, between the Y direct and reradiated waves, when account is taken of the phase reversal that occurs incidental to reflection or reradiation. Analogous conditions apply for transmission. y Such systems are inherently directional and may be made strictly unilaterally directive if made to ei'ect an amplitude as well as a phase balance. As an example of' such an arrangement, reference may be had toapplicants Patent 1,813,143, granted duly 7, 1931. l

VIt is an object of the invention to secure unilateral directivity, using a systemof spa-v cially related antenna units broadly as above, under conditions which would make the achievement of unidirectivity diliicult or imbe achieved entirely independently of such condition or other conditions alecting the geometry of the system except only the interspacing of the antennaunits.

As compared with prior systems of the above type or other directive antenna systems or apparatus, it is believed that applicants system excels in simplicity, economy of construction and eiliciency of operation as well as in the quality of directivity and it is a further object of the invention to provide an aerial system for space propagated waves which will have such characteristics.

According to the present invention the wave corresponding to the reflected or reradiated wave of the above described unilateral directive antenna system, instead of being reradiated to the receiving antenna proper, is returned to such antenna by a conductive pat-h interconnecting the antenna units at their lower terminals. This path constitutes a delay circuit for the wave propagated through it. The phase relation of the linally supcrposed waves depends on the electrical length ot the connecting path in relation to the lengths of theA antenna units through which also the cur 'ents corresponding to the elemental induced electroinotive forces induced by the incident waves are propagated as a delay circuit. lf the antenna units are each electrically half a w `ve length long and it they are spaced a quarter wave length or any odd multiple thereof, and it such interconnected circuit is electrically the same length as such spacing, the requisite condiions Will be satisfied so that the resultant superposed waves will have the proper phase with respect to a properly related receiver. As a practical matter these conditions may be satisfied if with the antenna spacing as above, theantenna units are simple conductors so that waves are propagated therealong with the velocity of other waves and if the connection circuit is similarly construct-ed and is connected by the shortest path between the lower extremities of the antenna units.

The operation of the same principle may alternatively involve the use ot different combinations ot electrical and physical dimensions, especially depending on the positioning of the connecting path. The two anteilna units may each have other forms than simple conductors, as above contemplated, so long as with respect to waves propagated in 5 the direction corresponding to the above antenna spacing, they function similarly thereto. For example, each such unit may have thc form of broadside antenna array of the form disclosed in the above identified co- .10 pending application.

of detail, while preserving the principle, more than one unit in addition to tl tt direct-ly vassociated with the receiver, may be used. The principle is equally applicable to transmitting systems.

The invention will be better understood from tl e following description taken in connection with the accompanying drawings forming a part thereof and in which: A

Figs. l and 2 each schematically illustrate a receiving system of the invention, and the electrical relations therein for particular direction of wave incid-ence, the two figures respectively illustratingthev condition most favorable for reception'and least favorable for reception; and o Fig. 3 illustrates schematically an alternative means for associating the receiver with the remaining circuits. l

Each of Figs. l and 2 represents symbolicvally a certain receiving antenna system of the invention, which is unilaterally directiveV with respect to incident waves propagated in two opposite directions in the plane of the two antenna unit-s AN1 and ANZ. ln Fig. l, as indicated, the incident wave is assumed to be propagated from right to left and therefore impinges on antenna ANl -efore it impinges on antenna ANZ, the converse being true with respect to Fig. 2. p

The waves impinging on h elemental portion of each of antennae ANZ and AN2 generate an electrornotive force therein which progresses as a wave in each direction to eventually reach ground at "G, the wave which is propagated downwardly being directly so transmitted and the wave which is correspondingly propagated upwardly. being flected at the upper free end ofthe antenna in uestion with a phase reversal and thence being propagated downwardly throughout' 50 assumed to be smallas compared. with the antenna interspacing, that is, as compared with the length of the connecting circuit and to be position-ed at the end thereof adjacent to the antenna AN1.

U5 -Of course -a certain interval of time is vrc- Also, by elaboration.

quired for the progression of an ether wave from a position in space corresponding to one antenna AN1 the corresponding position in space of the other antenna ANZ. In the example illustrated the inter-spacing is one quarter wavelength as indicated, so that the difference in time between the successive incidence of a given wave on the two antennae is one quarter period. However, in this Vdescription what will be particularly had in mind is the vphenomena occurring in the various parts of the system at a given instant of time. Therefore if at a certain instant of time a certain electroinotive force is being generated in antenna ANZ, at the same instant of time a corresponding electromotive force wave advanced inphase therefrom is being generated in antenna ANZ. The dashed arrows near the mid portions of the two antennae respectively indicate, as in accordance with the above, the vectors of the resultant electromotive forces el and eZ in antennae AN1 and ANZ,v due to the composition of the corresponding electromotive forces for the various elemental portions of the respective antennae. It is proper and convenient to thus consider-the effect as concentrated at the center. Of course the vectors are continuously rotating so that little significance attaches to the indicated position of each vector, per se, although their relation is ,denitive and is adequately shown. Counter-clockwise rotation is assumed to be positive so that the phaseof the wave eZis indicated as being 90 in advance of the phase ofthe wave el, as has been shown above to be correct. The antennae are assumedto be each half a wave length long, as indicated. This dimension is that for which the resultant electromotive force is a maX- imum. This is true for either short waves or long waves although ofcourse, as a practical matter, this ideal is not attainable with long waves of the usual order. The fact is immediately apparent when account is taken ofthe time lag of the elemental wavesfrom Ythe various elemental portionsprogressing Vto the bottom of an antenna, that is, where the receiver is located, superposed in the receiver.

It is an object of the vinvention to insure by properl geometrical andelectrical dimensions of the elements of the circuit that the waves corresponding to el and eZ afterpropagation from'the midpoints of the antenn and there being yto the receiver will be in phase with respect to waves propagated in a certain direction and will be opposite in phase with respect to waves propagated in the opposite direction. This condition defines unilateraldirectivity. The antennae and connecting circuit function as transmission lines for the propagation of these waves. As would be theV case with simple linear conductors illustrated it is assumed that they waves will be propagated over these conductors at the velocity of-space Waves so that a conductor of one quarter Wave length Vwill retard the Wave as much as, or acquire the same time for propagation therealong as, an equal distance in etheric space. l

The dashed arrow IDl and TID;

shown adjacent to ground indicatethe resultant phase at ground G of the 'propagated Wave initiated in the corresponding antenna AN1 and'AN2 respectively, and propagated directly to ground. Considering the conditions With respect to antenna AN1 there will be retardation of 90 on account of the one quarter Wave length of antenna through which the resultant electromotive force Wave e, must progress, so that, at the time of incidence of the Wave in the antenna and therefore When the phase of the electromotive force Wave el is that indicated by thel dashed arrow at the mid point of the antenna the phase of the vvave at therfoot of such antenna, and therefore at `ground, would have ay phase advanced 90 from the phase of the Wave el, as indicated. Correspondingly the Wave c2 propagated from the mid portionof antenna AN2 would bev retarded 90 on account of such an antenna and another 90 on account of the connecting circuit. The phase vector forthat antenna is accordingly indicated as advanced 180 over the vector for e2. It is noteworthy that the tWo vectors Iplialld Il)2 are Vin opposite phase. at the ground, that is, in the ground lead. The corresponding currents would therefore iow in the same direction in the ytwo portions of the inductance Lp on either side of the ground tap so that the Waves propagated to ground add their effects in the receiver connected to the secondary Ls. Following the same mode of reasoning with respectto Fig. 2, in Whichanv opposite direction of incidence of the ether Wave isv assumed, it will Vbe found that at ground the phases of the Waves corresponding to those discussed in the above paragraph is the same for the two antennze and therefore opposite in the two portions of the primary Lpfso .that their effects are opposed in the receiver connected to conductance Ls. f y t has thus been demonstrated with respect to Waves directly propagated from the antennae to the ground the system is unilaterally directive. It remains, however, to consider the effectof the Waves propagated upwardly in the antennae and reflected at the 'free ends. These Waves asmeasured atthe ground are illustrated by the dashed arrows IRl and .[32

Considering the conditions with respect to antenna ANl of Fig. 1 the Wave el as thus propagated is retarded90o ih progressing to the free end ofthe antenna, is then effectively retarded 180 by reflection, and is then retarded 180 3 by propagation along the entire length of the antenna, so that the phase of the propagated current at ground is 4500, that is, effectively 90. in advance of the phase of Wave e1 as indicated. By a similar course of reasoning it is apparent that the corresponding phase of the current propagated from the middle of antenna AN2 is 180 in advance of of the phase of the wave c2. This means that the two reflected Waves, similarly as the tivo direct Waves, are in opposite phase in the ground lead or in the same phase with respect to the receiver. It is also true that the reflected and direct waves are in the same phase. An analogous relation may easily be foundv with respect to the conditions illustrated by F ig. 2, that is, the reflected Waves affect the receiver in opposite directions and have the same phase as the direct Wave at the receiver. Accordingly it has been demonstrated that the system of Fig. l or Fig. 2 is unilaterally directive with respect to the reiected, as Well as the direct Waves and to such YWaves jointly and therefore with respect to all Waves which may affect the receiver.

It is obvious that the principle applied above to a specific instance, is much more generally applicable. For example, the principle is equally operative if the spacingr of the antennae is any other odd multiple of a one quarter wave length than the multiple one. Further it is possible to design the transmission line, comprising the connecting circuit and antenna proper. so that waves will be propagated there along at a velocity either greater or less than that of waves in space. Therefore it is possible to use antennae which are other than half a wave length long and a connecting circuit which is longer or shorter than the inter-antenna spacing. It is also obvious that the principle is equally applicable to a transmission system, the receiver in Figsl and 2 beingreplaced by aA transmitting source.

It has been assumed that the Waves directly transmitted or reflected at the receiver Will have the same amplitude, as they Would tend to have with the conditions as illustrated. Of course unilateral directivity in a strict sense requires that these amplitudes should be the same. They may be made exactly the same by an adjustment of the ground tap toward or away from the center of the inductance LP.

Fig. 3 illustrates an antenna system which is alternative to that ot' Figs. l and 2, the difference relating solely to the means or method. offassociating the` antenna-ground'.

paths with the receiver. Each of the antennnae 1s connected to ground through a resonant circuit as shown, which is tuned to the .frequency of the incident wave. The coils of 1 "of Figs. l and 2. A difference in addition to the use of such resonant circuits relates to the means for affecting the amplitude adjustment, which in the circuit of Fig. 3 is accomplished by the variable tap from the .antenna to the respective resonant circuit. VStill a third difference relates to the connection of the receiver to theseinductances. In Fig. 3

the receiver` is chrectly connected to the in-` ductance of one antenna and is magnetically coupled with the inductance of the other antenna 'insteadv of being magnetically coupled with each of the coils as in Figs. 1 and'2. The arrangement of Fig. 3 has been found to be vperhaps more convenient and generally satisfactory than that of Figs. l and 2.

rllhe system of Fig. 3 maybe made unilaterally directive inthe opposite direction by reversing the'connections to either coil or, nvhichamounts to the same thing, connecting the ground to the opposite end of either coil. Similarly the system of Figs. l and 2 may be made unilaterally directive in the opposite irection by connecting the coil LP in the .ground lead instead of in the position illustrated. These various changes have the common purpose and result of reversing the phase of one of the superposed currents with respect to the other. Y

.By elaboration of detail the principle of the invention may be made applicable to a.

similar relation of more than two antennaealthougli of course the quantitive eifects would tend to be different so thatthere would `be required quantitatively diiterent values of the physical dimensions to give the requisite amplitude phase unbalance.

What is claimed is: y Y l. The method of unilaterally directive radio reception which comprises absorbing a portion of a radio wave when at a given position in space, absorbing an additional portion ofthe wave when at a different position 5-sorbed Wave portions to a given point and there receiving them and indicating theiriel in space, independently transmitting the absultant effect, and shifting the phases of the respective absorbed portions by a critical amount such that the resultant eiect is a desired direction through said positions and zero for a radio wave propagated in the opposite direction through said positions.

2. The method of unilaterally direc-tive radio-operation, utilizing a plurality of radio antennae anda translating device, which coinprises transmitting portions .of a wave between said device-.and said antennae by as many independent paths as there are antennae guiding` the wavev portion over at least a part of each path and radiating it through the remaining part of thepath, and effecting such a relative retardation of the wave portions in the' respective paths that when said wave is transmitted outwardly from said device to said antennae and thence into space the resultant transmission is substantially Zero inone direction-and the maximum in the opposite direction, and so that similarlywhen said wave isabsorbed from an ether wave by said antennae and is transmitted inwardly therethrough to said device the resultant vwave at the device has substantially Zero amplitude with respect to ether waves propagated in Aone directionand a maximum .amplitude with respect toether waves propagated in the yopposite direction.

3. The method, of unilaterally directive p radio reception comprising absorbing radiant wave energy from two pointsin space, inde- 5,-'

pendently 'transmitting the energy absorbed from the respective points to a third point by wave propagated over' differentelectrical distances whereby there Vtends to resulta phase shift in the respective paths which is proportional to the corresponding electrical distance, and receiving and indicating the resultant effect of the transmitted waves at said third point, the relative electrical distances being such that the phases of the transmitted waves at the third point are alike when the original ether wave is propagated l in one direction and opposed when the ether wave is propagated in the opposite direction.

4. Anni-directional antenna system comprising two antennae,l Va translating device, and an individual transmission line connecting said device with each of said antennae, the ,'phase shift in the path between one antenna and the device by way of its transmission line being equal to the Vcorresponding phase shift in the path between the same' antenna andthe device" by way of the other antenna and its transmission line.

5.- A. uni-directional'antenna system comprising two antennae, the electrical length oin4 each antenna being an odd multiple of half a wave length of an ether wave to be used, said antennae also Vbeing .parallel and spaced a multiple of one quarteiyvvave length, a transslating device, a transmisssion line connecting the lower ends of the two antenn, said device being coupled to said transmission lineadjacent one end thereof whereby said device is connected tol one antenna by a trans- 1 luc Jhe system is a receiving system, said device therefor being a receiving and indicating means.

7. The arrangement of claim in which the system is a receiving systm, said device therefor being a receiving and indicating means.

In Witness whereof, I hereunto subscribe e my name this 1st day of June7 1928.

EDMOND BRUCE. 

